Polymer

ABSTRACT

The present invention relates to new semiconductive oligomers and polymers, a process for their manufacture and their use in thin film electronic and optical devices, such as organic light emitting diodes (OLED) and photovoltaic devices, eg. solar cells and photodetectors.

RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. 371)of PCT/EP2004/006721 filed Jun. 22, 2004 which claims benefit toEuropean application 03014042.0 filed Jun. 23, 2003.

FIELD OF THE INVENTION

This invention relates to semiconductive oligomers and polymers, theirsynthesis and use in thin film electronic and optical devices.

BACKGROUND OF THE INVENTION

Semiconducting organic materials are attracting a great deal of interestdue to their processability and the broad spectrum of optical andelectronic properties that may be selected according to the structure ofthe organic material.

One application of such materials is in switching devices, in particularas organic field effect transistors as described in, for example, Adv.Mater. 1998 10(5), 365-377.

Another application is in opto-electrical devices using a semiconductingorganic material for light emission (an organic light emitting device or“OLED”) or as the active component of a photocell or photodetector (a“photovoltaic” device). The basic structure of these devices is asemiconducting organic layer sandwiched between a cathode for injectingor accepting negative charge carriers (electrons) and an anode forinjecting or accepting positive charge carriers (holes) into the organiclayer.

In an organic electroluminescent device, electrons and holes areinjected into a layer of electroluminescent semiconducting materialwhere they combine to generate excitons that undergo radiative decay.Holes are injected from the anode into the highest occupied molecularorbital (HOMO) of the electroluminescent material; electrons areinjected from the cathode into the lowest unoccupied molecular orbital(LUMO) of the electroluminescent material. In WO 90/13148 the organiclight-emissive material is a polymer, namely poly(p-phenylenevinylene)(“PPV”). This class of device is commonly known as a polymer lightemitting device (PLED). In U.S. Pat. No. 4,539,507 the organiclight-emissive material is of the class known as small moleculematerials, such as (8-hydroxyquinoline) aluminium (“Alq₃”).

One alternative to PPVs are 2,7-linked polyfluorenes as disclosed in EP0842208 which have attracted attention because of their advantage ofsolution processability, such as suitability for inkjet printing.Furthermore, fluorene monomers with appropriate leaving groups areamenable to Suzuki or Yamamoto polymerisation. Suzuki polymerisation inparticular affords a great deal of control over the regioregularity andtherefore the properties of the polymer. Fluorene repeat units maytherefore be used as a “building block” in creating co-polymers with awide range of charge transporting and/or emissive properties.

However, there are a number of disadvantages associated withpolyfluorenes which have led to a search for alternative electrontransporting and light emitting units. These disadvantages include thetendency of polyfluorenes to aggregate and the fact that when blue lightemission occurs from fluorene based polymers the emission does not occurin the region of the electromagnetic spectrum in which the human eye ismost sensitive.

One alternative to fluorene repeat units are trans-indenofluorene repeatunits (illustrated below) as disclosed in, for example, Macromolecules2000, 33(6), 2016-2020 and Advanced Materials, 2001, 13, 1096-1099.

Polymers comprising the tetraoctyl trans-indenofluorene unit aredescribed as having

a bathochromically shifted emission wavelength which leads to a blueemission colour matched to the sensitivity of the human eye. However,poly(trans-indenofluorenes) have a lower conductivity than correspondingpolyfluorenes.

It is therefore an object of the invention to provide a repeat unit thatpossesses the advantages of trans-indenofluorene over fluorene withoutsuffering from loss of conduction.

SUMMARY OF THE INVENTION

The present inventors have surprisingly found that oligomers or polymerscomprising cis-indenofluorene repeat units have comparable or betterconduction than corresponding oligomers or polymers comprising fluorenerepeat units. Furthermore, the present inventors have surprisingly foundthat oligomers or polymers comprising cis-indenofluorene repeat unitsare blue-shifted relative to the corresponding oligomers or polymerscomprising trans-indenofluorene repeat units.

Accordingly, in a first aspect the invention provides an oligomer orpolymer comprising an optionally substituted first repeat unit offormula (Ir):

wherein R¹, R², R³ and R⁴, which may be the same or different, areindependently selected from hydrogen or a substituent and two or more ofR¹, R², R³ and R⁴ may be linked to form a ring.

Without wishing to be bound by any theory, it is believed that locatinggroups R¹, R², R³ and R⁴ on the same side of the repeat unit backboneenables close packing of oligomers or polymers containing the backbone,leading to improved conductivity, as compared to trans-indenofluorenerepeat units which have two substituent groups on one side of the repeatunit and two substituent groups on the opposite side of the backbone.Furthermore, the present inventors have found that there is a smalltwist within the repeat unit of formula (Ir) which is believed to be dueto steric interactions between groups R¹ and R² and groups R³ and R⁴.This twist, which is not present in the correspondingtrans-indenofluorene repeat unit; renders the cis-indenofluorene unit offormula (Ir) less prone to aggregation than a correspondingtrans-indenofluorene unit. Finally, this twist also blue-shifts thecolour of emission of oligomers or polymers comprising the repeat unitof formula (I) as compared to oligomers or polymers comprising repeatunits of trans-indenofluorenes.

Certain substituents R¹, R², R³ and R⁴ may modify the properties of therepeat unit, and therefore the polymer, such as its solubility, electronaffinity or glass transition temperature (Tg). Therefore, it ispreferred that each R¹, R², R³ and R⁴ is independently selected from thegroup consisting of optionally substituted alkyl, alkoxy, aryl, orheteroaryl. More preferably, at least one of R¹, R², R³ and R⁴ isoptionally substituted phenyl or optionally substituted C₁₋₂₀ alkyl.

Particularly preferred substituents are C₁₋₂₀ alkyl or alkoxy, inparticular branched alkyl or n-alkyl, such as n-octyl, as solubilisingsubstituents; optionally substituted phenyl or oligophenyl (e.g.biphenyl or terphenyl) as Tg increasing substituents, in particularunsubstituted phenyl, phenyl substituted with alkyl or alkoxy to improvesolubility and phenyl substituted with fluorine, fluoroalkyl,perfluoroalkyl to increase electron affinity; and optionallysubstituted, electron deficient heteroaryls in particular pyridine,pyrimidine and triazine, each of which may be unsubstituted orsubstituted with substituents listed as for phenyl above.

Asymmetry within the polymer may be desirable in order to minimise thepossibility of aggregation. Therefore, it is preferred that at least oneof R¹, R², R³ and R⁴ is different from at least one other of R¹, R², R³and R⁴. In one particularly preferred embodiment, R¹ and R² are bothoptionally substituted alkyl and R³ and R⁴ are both optionallysubstituted aryl. In another particularly preferred embodiment, R¹ andR³ are both optionally substituted alkyl and R² and R⁴ are bothoptionally substituted aryl.

Appropriate selection of the four substituents R¹, R², R³ and R⁴ enablesgreater control over the properties of the oligomer or polymer ascompared to corresponding fluorenes wherein there are only two suchsubstitution positions. Further modification of the properties of therepeat unit of the invention may be achieved by substitution of one ormore of the phenyl groups of the repeat unit of formula (Ir).Preferably, such substitution takes the form of a repeat unit of formula(II):

wherein at least one of R⁷ and R⁸ represents a substituent, and R⁷ andR⁸ together may form a ring.

In one preferred embodiment, R⁷ and R⁸ are both substituents and are thesame or different. Preferred substituents R⁷ and R⁸ are optionallysubstituted alkyl, alkoxy, aryl, or heteroaryl; particularly preferredsubstituents R⁷ and R⁸ are as described above with reference to R¹, R²,R³ and R⁴.

Preferably, the first repeat unit is linked through the 2- and9-positions as shown below (because this maximises conjugation throughthe repeat unit).

The polymer, according to the invention may be a homopolymer or aco-polymer. Where the polymer is a co-polymer wide range of propertiesmay be accessed by appropriate selection of co-repeat unit or co-repeatunits. Therefore, the oligomer or polymer preferably comprises a secondrepeat unit. Preferably, the second repeat unit comprises an aryl groupthat is directly conjugated to the first repeat unit. More preferably,the second repeat unit is selected from optionally substituted aryl,heteroaryl and triarylamine repeat units.

In a second aspect, the invention provides an optionally substitutedmonomer of formula (Im):

wherein R¹, R², R³ and R⁴, which may be the same or different, areindependently selected from hydrogen or a substituent and two or more ofR¹, R², R³ and R⁴ may be linked to form a ring; and each P represents apolymerisable group.

Advantageous polymerisation techniques include Suzuki and Yamamotopolymerisations which operate via a “metal insertion” wherein the metalatom of a metal complex catalyst is inserted between an aryl group and aleaving group of a monomer. Therefore, each P preferably represents aleaving group capable of participating in a polycondensation mediated bya metal of variable oxidation state.

Preferably, the polycondensation is mediated by a metal insertion.

Preferably, each P is independently selected from halogen; a moiety offormula —O—SO₂—Z wherein Z is selected from the group consisting ofoptionally substituted alkyl and aryl; or a reactive boron groupselected from a boronic acid, a boronic ester or a borane. Preferredhalogens are bromine, chlorine and iodine, more preferably bromine.

In a third aspect, the invention provides a process for preparing anoligomer or polymer comprising the step of oligomerising or polymerisinga monomer according to the second aspect of the invention.

In a first preferred embodiment of the third aspect, each P isindependently a halogen or a moiety of formula —O—SO₂—Z, wherein Z isselected from the group consisting of optionally substituted alkyl andaryl, and the monomer of formula (III) is oligomerised or polymerised inthe presence of a nickel complex catalyst.

In a second preferred embodiment of the third aspect, the monomer offormula (III) is oligomerised or polymerised with a second aromaticmonomer in the presence of a palladium complex catalyst and a base and

-   -   (a) each P is the same or different and comprises a reactive        boronic group and the second monomer comprises two reactive        groups independently selected from halogen and a moiety of        formula —O—SO₂—Z, or    -   (b) each P independently comprises a halogen or a moiety of        formula —O—SO₂—Z and the second monomer comprises two reactive        boron groups which are the same or different.

In a third preferred embodiment of the third aspect, one P is a reactiveboron group and the other P is a halogen or a moiety of formula—O—SO₂—Z.

In a fourth aspect, the invention provides an optical device comprisingan oligomer or polymer according to the first aspect of the invention.Preferably, the oligomer or polymer is located between a first electrodefor injection of charge carriers of a first type and a second electrodefor injection of charge carriers of a second type.

In addition to their applicability in optical devices such as OLEDs orphotovoltaic devices, the oligomers or polymers according to theinvention may be used in a switching device. Accordingly, in a fifthaspect the invention provides a switching device comprising an oligomeror polymer according to the first aspect of the invention. In apreferred embodiment, this aspect of the invention provides a fieldeffect transistor comprising an insulator having a first side and asecond side; a gate electrode located on the first side of theinsulator; an oligomer or polymer according to the first aspect of theinvention located on the second side of the insulator; and a drainelectrode and a source electrode located on the oligomer or polymer.

In a sixth aspect, the invention provides an integrated circuitcomprising a field effect transistor according to the fifth aspect ofthe invention.

In a seventh aspect, the invention provides A method of forming anoptionally substituted compound of formula (I):

comprising the step of eliminating LG-H from an optionally substitutedcompound of formula (Ip):

wherein each LG is the same or different and represents a leaving group.

Suitable leaving groups include halide, —OR, —SR, —OSO₂R and —NR₂wherein each R independently represents hydrogen or optionallysubstituted alkyl or aryl. Preferably, each LG is hydroxy.

Preferably, the elimination is performed in the presence of an acid.

Preferably, the acid is polyphosphoric acid.

Preferably, the method comprises the further step of providing apolymerisable group P on each of the outer phenyl rings of the compoundof formula (I) or (Ip).

DETAILED DESCRIPTION OF THE INVENTION

Oligomers and polymers according to the invention may be used assolution processable, electron transporting, hole transporting and/oremissive materials in organic light emitting devices. The invention isdescribed hereinafter with reference to polymers, however it will beappreciated that features described herein may apply equally tooligomers.

The polymers may be prepared by Suzuki polymerisation as described in,for example, WO 00/53656 or WO 03/048225 and Yamamoto polymerisation asdescribed in, for example, T. Yamamoto, “Electrically Conducting AndThermally Stable π-Conjugated Polyarylenes Prepared by OrganometallicProcesses”, Progress in Polymer Science 1993, 17, 1153-1205 or WO04/022626. For example, in the synthesis of a linear polymer by Yamamotopolymerisation, a monomer having two reactive halide groups P is used.Similarly, according to the method of Suzuki polymerisation, at leastone reactive group P is a reactive boron group.

Suzuki polymerisation employs a Pd(0) complex or a Pd(II) salt. Pd(0)complexes are preferred, in particular Pd(0) complexes bearing at leastone phosphine ligand such as Pd(Ph₃P)₄. Suzuki polymerisation isperformed in the presence of a base, for example sodium carbonate or anorganic base such as tetraethylammonium carbonate.

Yamamoto polymerisation employs a Ni(0) complex, for examplebis(1,5-cyclooctadienyl)nickel(0).

Suzuki polymerisation may be used to prepare regioregular, block andrandom copolymers. In particular, homopolymers or random copolymers maybe prepared when one reactive group P is a halogen and the otherreactive group P is a reactive boron group. Alternatively, block orregioregular, in particular AB, copolymers may be prepared when bothreactive groups of a first monomer are boron and both reactive groups ofa second monomer are halide.

The monomer according to the invention may be polymerised alone to forma homopolymer or in the presence of one or more co-monomers to form aco-polymer. Possible co-repeat units derived from such co-monomers areoutlined below; it will be appreciated that each of these co-repeatunits may be derived from a comonomer comprising two polymerisablegroups independently selected from halogen (preferably chlorine, bromineor iodine, more preferably bromine), a boronic acid group, a boronicester group and a borane group.

As alternatives to halogens as described above, leaving groups such astosylate, mesylate and triflate may also be used.

Where the polymer according to the invention is a co-polymer, one classof co-repeat units is arylene repeat units, in particular: 1,4-phenylenerepeat units as disclosed in J. Appl. Phys. 1996, 79, 934; fluorenerepeat units as disclosed in EP 0842208, trans-indenofluorene repeatunits as disclosed in, for example, Macromolecules 2000, 33(6),2016-2020 and spirobifluorene repeat units as disclosed in, for exampleEP 0707020. Each of these repeat units is optionally substituted.Examples of substituents include solubilising groups such as C₁₋₂₀ alkylor alkoxy; electron withdrawing groups such as fluorine, nitro or cyano;and substituents for increasing glass transition temperature (Tg) of thepolymer such as bulky groups, e.g. tert-butyl.

A further class of preferred co-repeat units are repeat units comprisingone or two amino groups in the repeat unit backbone such as co-repeatunits comprising triarylamine groups, in particular repeat units offormulae 1-6:

X and Y may be the same or different and are substituent groups. A, B, Cand D may be the same or different and are substituent groups. It ispreferred that one or more of X, Y, A, B, C and D is independentlyselected from the group consisting of alkyl, aryl, perfluoroalkyl,thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl and arylalkyl groups.One or more of X, Y, A, B, C and D also may be hydrogen. It is preferredthat one or more of X, Y, A, B, C and D is independently anunsubstituted, isobutyl group, an n-alkyl, an n-alkoxy or atrifluoromethyl group because they are suitable for helping to selectthe HOMO level and/or for improving solubility of the polymer.

Use of trifluoromethyl groups in repeat units of this type is disclosedin WO 01/66618.

A yet further class of co-repeat units include heteroaryl repeat unitssuch as optionally substituted 2,5-thienyl, pyridyl, diazine, triazine,azole, diazole, triazole, oxazole or oxadiazole; or optionallysubstituted units of formulae 7-19:

wherein R⁵ and R⁶ are the same or different and are each independently asubstituent group. Preferably, one or more of R⁵ or R⁶ may be selectedfrom hydrogen, alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy,heteroaryl, alkylaryl, or arylalkyl. These groups are preferred for thesame reasons as discussed in relation to X, Y, A, B, C and D above.Preferably, for practical reasons, R⁵ and R⁶ are the same.

When used in an OLED, polymers according to the invention possess atleast one of hole transporting, electron transporting and emissiveproperties. Where the polymer has more than one of these properties,different properties may be provided by different segments of a blockco-polymer, in particular segments of the polymer backbone as describedin WO 00/55927 or pendant groups as described in WO 02/26859.Alternatively, if the polymer of the invention has only one or two ofthe properties of hole transport, electron transport and emission, itmay be blended with one or more further polymers having the remainingrequired property or properties as described in WO 99/48160.

Polymers according to the invention may be used as active materials inany of the aforementioned optical devices, in particularelectroluminescent devices and photovoltaic devices (i.e. photodetectorsor photocells). Such optical devices comprise a substrate carrying thepolymer located between a positive charge carrying electrode and anegative charge carrying electrode. In forming these devices, thepolymer may be deposited from solution by any one of a range oftechniques including in particular techniques such as spin-coating,dip-coating, inkjet printing as disclosed in EP 0880303, laser transferas described in EP 0851714, flexographic printing, screen printing anddoctor blade coating.

Optical devices tend to be sensitive to moisture and oxygen.Accordingly, the substrate of the device preferably has good barrierproperties for prevention of ingress of moisture and oxygen into thedevice. The substrate is commonly glass, however alternative substratesmay be used, in particular where flexibility of the device is desirable.For example, the substrate may comprise a plastic as in U.S. Pat. No.6,268,695 which discloses a substrate of alternating plastic and barrierlayers or a laminate of thin glass and plastic as disclosed in EP0949850.

Although not essential, the presence of a layer of organic holeinjection material over the anode is desirable as it assists holeinjection from the anode into the layer or layers of semiconductingpolymer. Examples of organic hole injection materials include PEDT/PSSas disclosed in EP 0901176 and EP 0947123, or polyaniline as disclosedin U.S. Pat. No. 5,723,873 and 5,798,170.

The cathode is selected in order that electrons are efficiently injectedinto the device and as such may comprise a single conductive materialsuch as a layer of aluminium. Alternatively, it may comprise a pluralityof metals, for example a bilayer of calcium and aluminium as disclosedin WO 98/10621, or a thin layer of dielectric material such as lithiumfluoride to assist electron injection as disclosed in, for example, WO00/48258.

The device is preferably encapsulated with an encapsulant to preventingress of moisture and oxygen. Suitable encapsulants include a sheet ofglass, films having suitable barrier properties such as alternatingstacks of polymer and dielectric as disclosed in, for example, WO01/81649 or an airtight container as disclosed in, for example, WO01/19142.

In a practical optoelectronic device, at least one of the electrodes issemi-transparent in order that light may be absorbed (in the case of aphotoresponsive device) or emitted (in the case of a PLED). Where theanode is transparent, it typically comprises indium tin oxide. Examplesof transparent cathodes are disclosed in, for example, GB 2348316. Wherethe polymer of the invention is used in a switching device such as afield effect transistor, it will be appreciated that all of theelectrodes may be opaque.

The PLED may be a passive matrix or active matrix device.

EXAMPLES Monomer Example

A monomer according to the invention was prepared in accordance with thescheme set out below:

Synthesis of Diene, St1

1,4-Diphenyl-1,3-butadiene (500 g, 2.42 moles) anddimethylacetylenedicarboxylate (378 g, 2.66 moles) were charged to a 2 Lvessel. Toluene (750 ml) was added and the mixture heated to reflux (oilbath temperature 145° C., diene dissolved >90° C.). The reaction wasrefluxed for 20 h (overnight) before being cooled to room temperature.Evaporation of the toluene afforded a yellow/brown solid, which wasrecrystallised from 2-propanol to give 780 g, 92.5% yield of the desiredproduct as a white solid. GC-MS gave a single peak m/z 348, HPLC 99.3%;¹H NMR 3.54 (6H, s, 2×CH₃), 4.47 (2H, s), 5.77 (2H, S), 7.24-7.34 (10H,m).

Synthesis of Terphenyl Cis-dimethylester, St2

To a toluene (100 ml) solution of the diene (stage 1 product, 10 g, 28.7mmol) was added palladium 10 wt. % on activated carbon (1.5 g, 10% wt).The reaction was refluxed (oil bath 130° C.) for 20 h (overnight). Thereaction was cooled slightly (80° C.) and diluted with toluene (100 ml)before hot filtering through a pad of celite filter agent. The filtercake was washed with a further 500 ml hot toluene to remove all of theproduct. Cooling of the filtrate crystallised the desired product as awhite solid 7.75 g, 78%. GC-MS≧95%, m/z 346; ¹H NMR 3.62 (6H, s, 2×CH₃),7.36-7.45 (10H, m), 7.52 (2H, s).

Synthesis of Terphenyl Cis diol, St3, St3B

A solution of diester (10 g, 17.56 mmol) in dichloromethane (130 mL) wasadded dropwise over 1 hour into a solution of diisobutylaluminiumhydride (1 M in hexane). After 2 h of stirring at roomtemperature the reaction was quenched, pouring the reaction mixture intoa saturated solution of ammonium chloride. The desired product wasextracted into dichloromethane (20 mL MeOH added). The organic layer wasdried (MgSO₄) and evaporated under vacuum affording 6.45 g (77% yield)of desired product. GC-MS confirmed 90% conversion to the diol and 10%of starting material remaining. ¹H NMR 2.925 (2H, OH), 4.78 (4H, s,CH₂OH), 7.34-7.46 (12H).

Synthesis of Cis indenofluorene, St5

The white dibenzylic alcohol (2.65 g, 9.1 mmol) was added topolyphosphoric acid (12 g) and heated to 180° C. Once at temperature thePPA became liquid and the white powder turned yellow. The reactionmixture was cooled to room temperature and then treated with a 10%solution of NaOH. 2.213 g (95% yield) of cis indenofluorene precipitatedout as a grey/white solid; GC-MS indicated 98% of desired material and2% of mono cyclised (St3B); ¹H NMR 3.95 (4H, S, CH₂×2), 7.31 (2H, t, J7.2), 7.39 (2H, t,-J 7.2), 7.59 (2H, d, J 8.0), 7.82 (2H, s), 7.83 (2H,d, J 7.2); ¹³C NMR 35.738, 118.954, 120.167, 125.374, 126.746, 127.089,139.593, 141.057, 142.307, 143.306.

Synthesis of St5

To a cooled (−78° C.) solution of cis indenofluorene (2 g, 7.9 mmol) inTHF (120 mL) was added BuLi (2.5M, 17.38 mmol). After addition wascomplete, the reaction mixture was left to stir at −78° C. for a further2 h and then left to warm to room temperature. The reaction mixture wasthen re-cooled to −78° C. and octyl bromide (3.26 mL, 18.96 mmol) added.The reaction mixture was allowed to room temperature over night and thewhole lithiation and alkylation process repeated. The reaction waspoured onto a mixture of petroleum ether-Et₂O and washed with H₂O. Theorganic layer was isolated, dried (MgSO₄) and the excess octylbromide/octane removed using Kugel distillation (40° C., 10⁻² mbar).GC-MS indicated 81% dialkyl and 15% trialkylated product. The isolatedmixed product (1.34 g) was put through the lithiation-alkylationprocedure again. To afford the desired tetra-alkylated product the wholeexperimental procedure was repeated using a further 5.2 equivalents ofBuLi and 6 equivalent of octyl bromide. 1.069 g of desired material wasisolated and used crude in the next stage. ¹H NMR 0.4-1.4 (30H), 2.2(2H, td, J 4.4, 12.8), 2.4 (2H, td, J 4.4, 12.8), 7.26-7.33 (6H, m),7.70 (2H, d, J 7.6), 7.74 (2H, s); ¹³C NMR 14.29, 22.84, 24.30, 29.68,29.82, 30.32, 32.05, 40.88, 58.24, 119.05, 119.130, 121.78, 126.79,127.24, 141.16, 142.30, 146.49, 150.98.

Synthesis of Monomer 1

To a 0° C. solution of St5 (1.069 g), iodine (catalytic) in CH₂Cl₂ (25mL) was added a solution of Na₂CO₃ (0.387 g) in H₂O (6 mL). Afterstirring for 5 minutes, bromine (183 μL) was added dropwise. Thereaction mixture was left to stir overnight. The reaction was treatedwith a 10% sodium thiosulphate solution (20 mL). The organic layer wasremoved, washed with water (2×20 mL). The organic layer was separatedfrom the aqueous, dried (MgSO₄Y and evaporated under vacuum. Columnchromatography elute hexane gave 450 mg of mono and di brominatedproduct; confirmed by GC-MS. This mixture was subjected again tobromination.

Indenofluorene repeat units carrying substituents on the central phenylring of the repeat unit were prepared in accordance with the followingscheme:

In addition to providing substituents on the central ring, the centralring of the monomer may comprise a fused ring, as illustrated belowwherein the central ring is a benzothiadiazole. The first step may beperformed by Suzuki coupling of the starting dibromo compound with twoequivalents of a phenyl boronic ester.

Finally, cis-indenofluorene monomers carrying different substituentsR¹-R⁴ were prepared in accordance with the following scheme. As shown inthe scheme, asymmetric substitution at the 11 and 12 positions wasaccomplished by forming an amide as described in Weinreb, TetrahedronLetters 22(39), 3815-3818, 1981; reacting the amide with one equivalentof a first alkyl, aryl or heteroaryl lithium to form a ketone; andreacting the ketone with one equivalent of a second alkyl, aryl orheteroaryl lithium that is different from the first alkyl, aryl orheteroaryl lithium.

Polymer Examples

Polymers according to the invention were prepared in accordance with themethod set forth in WO 00/53656 by polymerisation of the monomers shownbelow. Boronic esters were derived from Monomer 1 in accordance with themethod set forth in WO 00/53656.

For the purpose of comparison, polymers were prepared as per polymer 5above except that the following trans-indenofluorene monomers were usedin place of the cis-indenofluorene repeat unit according to theinvention:

Device Example

Onto indium tin oxide supported on a glass substrate (available fromApplied Films, Colorado, USA) was deposited a film of poly(ethylenedioxythiophene) (PEDT/PSS), available from Bayer® as Baytron P®, by spincoating. The electroluminescent layer was formed over the layer ofPEDT/PSS by spin coating from xylene solution comprising polymer 5according to the invention. A bilayer cathode of calcium/aluminium wasdeposited over the electroluminescent layer and the device wasencapsulated using an airtight metal enclosure containing a desiccantavailable from Saes Getters SpA.

For the purpose of comparison, identical devices were prepared exceptthat comparative polymers 6, 7, 8 and 9 were used in place of polymer 5.Device performance for the devices prepared from these materials issummarised in Table 1 below.

TABLE 1 Half life¹ % V at 100 from Colour Burn- Polymer CIEx CIEy cd/m²800 cd/m² Shift² Δ V³ in⁴ 5 0.16 0.17 4.3 120 h  0.03 1.0 3% 6 0.17 0.225.7 140 h  0.06 2.8 12% 7 0.16 0.19 5.1 46 h 0.04 0.2 24% 8 0.17 0.235.4 35 h 0.02 0.0 20% 9 0.17 0.22 5.4 70 h 0.06 0.6 1% ¹Half-life = timetaken for luminance to fall by half at constant current. ²Colour shiftmeasured at half-life and taking into account the lateral CIEx and CIEyshift from the starting colours, measured as the square root of: (CIExcolour shift)² + (CIEy colour shift)² ³Change in drive voltage duringthe half life of the device. ⁴Burn-in refers to an initial fall inluminance when the device is driven followed by a more gradual decay inluminance.

As can be seen from Table 1, polymer 5 according to the inventionprovides the best performance across the range of parameters measured.For most parameters, polymer 5 is superior to the comparative polymers;for the remaining parameters, there is no instance where the performanceof polymer 5 is significantly poorer than any of the comparativepolymers.

Although the present invention has been described in terms of specificexemplary embodiments, it will be appreciated that variousmodifications, alterations and/or combinations of features disclosedherein will be apparent to those skilled in the art without departingfrom the spirit and scope of the invention as set forth in the followingclaims.

1. An oligomer or polymer comprising an optionally substituted firstrepeat unit of formula (Ir):

wherein R¹, R², R³ and R⁴, which may be the same or different, areindependently selected from hydrogen or a substituent and two or more ofR¹, R², R³ and R⁴ may be linked to form a ring and the oligomer orpolymer comprises a second repeat unit.
 2. An oligomer or polymeraccording to claim 1 wherein each R¹, R², R³ and R⁴ is independentlyselected from the group consisting of optionally substituted alkyl,alkoxy, aryl, or heteroaryl.
 3. An oligomer or polymer according toclaim 1, wherein at least one of R¹, R², R³ and R⁴ is optionallysubstituted phenyl or optionally substituted C₁₋₂₀ alkyl.
 4. An oligomeror polymer according to claim 3 wherein at least one R¹, R², R³ and R⁴is different from at least one other R¹, R², R³ and R⁴.
 5. An oligomeror polymer according to claim 1, wherein the second repeat unit isselected from optionally substituted aryl, heteroaryl and triarylaminerepeat units.
 6. An optionally substituted monomer of formula (Im):

wherein R¹, R², R³ and R⁴, which may be the same or different, areindependently selected from hydrogen or a substituent and two or more ofR¹, R², R³ and R⁴ may be linked to form a ring; and each P represents apolymerisable group.
 7. A monomer according to claim 6 wherein each Prepresents a leaving group capable of participating in apolycondensation mediated by a metal of variable oxidation state.
 8. Amonomer according to claim 7 wherein each P is independently selectedfrom halogen; a moiety of formula —O—SO₂—Z wherein Z is selected fromthe group consisting of optionally substituted alkyl and aryl; or areactive boron group selected from a boronic acid, a boronic ester or aborane.
 9. A process for preparing an oligomer or polymer comprising thestep of oligomerising or polymerising a monomer according to claim 6.10. A process for preparing an oligomer or polymer according to claim 9wherein each P is independently a halogen or a moiety of formula—O—SO₂—Z, and the monomer of formula (Im) is oligomerised or polymerisedin the presence of a nickel complex catalyst.
 11. A process forpreparing a polymer according to claim 9 wherein the monomer of formula(Im) is oligomerised or polymerised with a second aromatic monomer inthe presence of a palladium complex catalyst and a base and a. each P isthe same or different and comprises a reactive boronic group and thesecond monomer comprises two reactive groups independently selected fromhalogen and a moiety of formula —O—SO₂—Z, or b. each P independentlycomprises a halogen or a moiety of formula —O—SO₂—Z and the secondmonomer comprises two reactive boron groups which are the same ordifferent.
 12. A process for preparing an ohgomer or polymer accordingto claim 9, wherein one P is a reactive boron group and the other P is ahalogen or a moiety of formula —O—SO₂—Z.
 13. An optical devicecomprising an oligomer or polymer according to claim
 1. 14. An opticaldevice according to claim 13 wherein the oligomer or polymer is locatedbetween a first electrode for injection of charge carriers of a firsttype and a second electrode for injection of charge carriers of a secondtype.
 15. A switching device comprising an oligomer or polymer accordingto claim
 1. 16. A field effect transistor comprising an insulator havinga first side and a second side; a gate electrode located on the firstside of the insulator; an oligomer or polymer according to claim 1located on the second side of the insulator; and a drain electrode and asource electrode located on the oligomer or polymer.
 17. An integratedcircuit comprising a field effect transistor according to claim
 16. 18.A polymer comprising an optionally substituted first repeat unit offormula (Ir):

wherein R¹, R², R³ and R⁴, which may be the same or different, areindependently selected from hydrogen or a substituent and two or more ofR¹, R², R³ and R⁴ may be linked to form a ring and the oligomer orpolymer comprises a second repeat unit.